Description of the Prior Art
Among the various types of fuel cell systems are those which include subassemblies of two bipolar plates between which is supported an acid electrolyte in a matrix. The subassemblies, herein referred to as fuel cells, are oriented one atop another and electrically connected, typically in series, to form a fuel cell stack. Operation of the fuel cell, for example, the reaction of hydrogen and oxygen to produce heat, electrical energy and water, is exothermic, and cooling of the cell components is necessary in order to maintain component integrity. Liquid or gaseous cooling fluids have therefore been passed through the stack to remove heat. Accordingly, three fluid mediums, a fuel, an oxidant and a cooling fluid flow in some manner into and out of the fuel cell stack.
As a result of system design limitations, such as the geometric configuration and the need to provide sufficient cooling, fluid streams have typically been combined or require relatively complex sealed ducting configurations to direct flow of the various fluid mediums. For example, systems have been proposed wherein the cooling fluid and oxidant are the same medium, such as air. Such systems require a high circulatory power, detracting from overall system efficiency, and can subject downstream components, such as heat exchangers, to undesirable reaction products carried with the depleted oxidant. Further, in combined systems providing energy generation utilizing the waste heat removed from the fuel cell stack, it is desirable to recover the heat at a high temperature, which is limited by excessive air flow rates. Other systems, such as that described in U.S. Patent No. 4,074,020, require flow paths which enter a longitudinal end of the stack, flow radially through selected sections of the stack, and are discharged longitudinally, creating multiple flow paths and large pressure drops. Multiple, spaced inlets and outlets also require complex ducting.
Accordingly, it is desirable to provide fuel cell systems which alleviate these concerns. Such systems advantageously should simplify system construction and promote system efficiency.